Can a 3.5" HDD be enclosed in an external USB-C enclosure with USB-C Power Delivery [PD] and have a USB-C cable from the computer as the only power source to avoid a second power cable?

Does such a case exist?

  • 2
    The question is, is there even any usb host port is a PD source? Let alone the possibility of making use of that to provide the 12v rail in addition to the 5v rail
    – Tom Yan
    Jun 23, 2021 at 9:06
  • 1
    Whether such a case exists, I'm unsure, but it's possible provided the USB-C power source outputs 12v @ ~1A [V*A=W], however high output USB-C power ports are usually for laptops and output at voltages >12v, so voltage negotiation would be required; this requires either the enclosure to be QC [Quick Charge] compatible or the power source to have some mechanism to auto/manually determine 12V is all that should be output (voltage is pressure, amperage [current] is how much pressure is being allowed through, so at a certain voltage higher than 12v, it'll fry the PCB)
    – JW0914
    Jun 23, 2021 at 12:11
  • 1
    @Robert PD can go up to 20v. It's just I'm not sure whether it can provide both the 5v and 12v rails at the same time (or whether most/all 3.5" HDD can work with only the 12v one). Nevertheless, I doubt that any enclosure vendor will make use of PD for the 12v rail anyway (not even with a separate USB-C power input port).
    – Tom Yan
    Jun 23, 2021 at 12:11
  • 2
    @TomYan As far as I know USB-C can not deliver different power level at the same time. In set-up phase both sides agree on a power level and that is then used. The USB enclosure would have to use 12V and generate 5V from it.
    – Robert
    Jun 23, 2021 at 12:54
  • 2
    @Robert Yeah, that's what I would presume, which is a major reason that I don't think the vendors would bother (/ can handle).
    – Tom Yan
    Jun 23, 2021 at 13:10

3 Answers 3


Looking at some old 3.5" HDDs I have stacked in my basement I see that they require less than 1 amp on both the 5 volt and 12 volt DC input pins, most less than 1/2 an amp. This means they will take less than the 15 watts that many USB-C ports on many computers can supply, and many less than the 7.5 watts that is the minimum a USB-C port must provide to meet the USB-C spec.

A problem with this is that the ports on most computers will only supply 5 volts, and the drives will need 12 volts. It is possible to have a voltage boost circuit to create the 12 volt supply but that is an expensive circuit to build in the thin margins of consumer electronics. It is far less expensive to build a buck circuit to take a higher voltage to a lower voltage, and that's how some enclosures get the 3.3 volts that some drives use off a 5 volt supply from USB-C or USB-A.

It is unlikely such cases exist on the market. The profit margins are thin and the power budget is thin. The people making the cases must assume 5 volts at 1.5 amps from the USB-C port as that is the specified minimum for USB-C compliance. 3 amps from USB-C is common but not universal. 12 volts from USB-C was optional in USB-PD 1.0 but 5 years later became deprecated in favor of 9 volts and 15 volts when USB-PD 2.0 was published. USB-PD 1.0 was not very popular for some reason, it seems the people behind USB would rather everyone forgot it existed.

If we assume that the case for a 3.5" HDD must have room for 12 volts at 1 amp for the drive then that right there takes 12 watts. Then comes the 5 volt supply which might take 1/2 an amp, 2.5 watts. Then the interface board will need power. That's cutting it close even if the people engineering the case know that there will be 15 watts available.

The question did specify use of USB-PD for the drive enclosure power. USB-PD is only required if the client device is going to ask for more power than the 5 volts at 3 amps allowed with the USB 3.x spec. In most computers there will be a 12 volt supply but, again, supplying this out the USB-C port is not part of the current spec. It is allowed for backward compatibility to USB-PD 1.0 devices but, shall we say, "discouraged". Boosting that up to 15 volts is possible, then in the drive it can be bucked down to 12 volts and 5 volts easily enough. The USB-C ports on most computers that claim "high power" will be 15 watts (5 volts at 3 amps) or maybe 27 watts (9 volts at 3 amps). If they provide 12 volts then it's at most 27 watts, or 2.25 amps. Then after the 12 volts gets to the drive maybe there is more than 2 amps to work with, or maybe not because 2.25 amps is a maximum and not a minimum.

The thin power margins on USB-C under USB 3.x makes it difficult to power a 3.5" HDD. Requiring USB-PD for power means very few buyers as USB-PD output on computers is slim to none, and people willing to pay extra to not need an external power supply will also be slim to none. If such an enclosure exists then I'd be very surprised.

  • Is it really the case that a buck converter is "far less expensive" than a boost converter, roughly speaking? I would have thought that they would use a single linear regulator IC to drop 5V down to 3.3V, instead. Jul 5, 2022 at 20:04

USB C PD 2.0 dropped mandatory 12V (and PD 1.0 is a paper only standard) and made that voltage optional. So our theoretical enclosure would only work with certain power supplies which is annoying and it's not possible for the end user to easily tell from the wattage alone. For eg. I have a non-spec compliant laptop which requires 12V 2.5A over USB C to charge and it's a major annoyance to figure out which 30W power banks can supply it. PD 3.0 introduced PPS which would be another source of 12V but again some chargers implement it and some don't.

Looking at How much power does a hard drive use? we can see some hard drives use above 20W when spinning up which means even if we tried to boost the voltage of the max 15W 5V supply, it wouldn't be enough always. While that is old, looking at more modern hard drives say 6-14TB WD Red Plus 1.75A-1.85A maximum is still there.

So you would have an enclosure which doesn't always work which would make customers unhappy, review scores low and support costs high. This is a no go.

Another solution would be to make the enclosure a full docking station: take 20V 5A, negotiate with the laptop for 65W max and use the remaining wattage by converting the 20V down to 12V. I speculate when I say the cost of this would probably make such a thing not alluring to consumers especially when compared to the really low cost separately powered HDD enclosures so no one bothered to make one.

You could, of course, use 15V and make the enclosure standalone but once you add a voltage converter circuit the relative added cost of another USB C PD controller is very low and the results would make more sense because if you are powering the enclosure and the laptop separately, what's the point of using USB C power for the enclosure...?


USB type is supposed to be able to supply 100w or 20v at 5amps.

It is physically possible to design a circuit to request the necessary power to provide all the power necessary to run a 3.5" hard drive.

1 amp at 5v is 5w and 1 amps at 12v is 12w. So the total is 17w. Now there will be a power loss in the conversion process, but if your USB type C port actually provides 100w there is a large margin of error.

However, the BIG problem is not every USB type C port is actually 100% compliant. Many don't offer the 100w option, but if yours does it is possible.

Now I don't know if anyone has actually done this or not.

  • Are you saying that by not offering 100 watts of power output a USB-C port does not comply with the USB-C spec? The spec only requires 5V @ 1.5A, anything beyond that is optional. Indeed, a USB-C port is able to supply up to 20V @ 5A but that is different from a port must supply that much power.
    – MacGuffin
    Jun 26, 2021 at 11:00
  • @MacGuffin The USB standard committee has only made our lives miserable but allow this all these non-sense modes. Every USB type C port should be capable of 100w, so as to not create consumer confusion. USB 2 was 100% clear 500ma max, and USB 3 was equally clear with 900ma max. I should not have to have 15 different USB type C adapter to make sure I have one that I can use with any device. So now I have to do 100's of hours of research to make sure I am buying the right thing, consumers shouldn't have to worry about this.
    – cybernard
    Jun 27, 2021 at 15:20
  • Having read many of the USB specification documents I find them to be quite logical. What makes people "miserable" in my opinion are the people that make devices that do not follow the spec. The USB people deserve some criticism for the short lived mini connectors, they were poorly designed and they should have known that. What makes me "miserable" about it are manufacturers that keep using them even though the USB group declared mini ports a dead end. If everyone followed the spec then people would be less "miserable".
    – MacGuffin
    Jun 28, 2021 at 6:42

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